Mill for grinding and sheeting rubber



NQG. MITCHELL. MILL FOR GRINDING AND SHBETING RUBBER. No. 408,734.

(No Model.)

Patented Aug. 13, 1889..

UNITED STATES P TENT OFFICE.

NATHANIEL Ol-IAPMAN MITCHELL, OF PHILADELPHIA, PENNSYLVANIA.

MILL FOR GRINDING AND SHEETING RUBBE R.

SPECIFICATION forming part of Letters Patent No. 408,734, dated August 13, 1889. Application filed May 28, 1889. Serial No. 312,375. (No model.) i

To all whom it may concern.-

Be it known that I, NATHANIEL CHAPMAN MITCHELL, of Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented a new and useful Improvement in Mills for Grinding and Sheeting Rubber, which improvement is fully set forth in the following specification.

This invention relates to the construction of mills or' machines used in rubber-manufacture for refining and sheeting rubber, and is more particularly intended for use in connection with devulcanized rubber reclaimed from boots and shoes, belting, hose, and other articles.

The object of the invention, generally stated, is to increase largely the capacity of grinding-mills, thereby effecting an important saving in the industry. It also aims to render such mills less dangerous to the workmen in removing the sheeted product.

As the process of sheeting is at present carried on, the output of a mill is limited by the speed at which the grinding-rolls can practically be driven. The maximum speed at present attainable is about fourteen to fifteen revolutions per minute. Even at this comparatively slow rate the heat developed by friction is very great, and this heat is of course communicated by the rolls to the rubber passing between and around them. The attempt to run the mill at a greater speed than above indicated results in injury to the rubber. Even at the moderate speed at which the mills are now worked the rubber becomes so hot as to be difficult to handle, and, moreover, it adheres so tenaciously to the surface of the roll as to render its removal a work of some time and trouble. When the sheeting operation is concluded, the operator must sever the-sheet by cutting through it with a knife across its full width, (frequently having to make several cuts,) and then pull with considerable force to detach the rubber from the roll. This operation, moreover, is dangerous, and accidents to workmen by having their hands pulled into the nip of the rolls are of frequent occurrence. I

My invention consists in the combination, with the grinding and sheeting rolls, of means whereby the rubber sheet is kept out of contact with such rolls except when passing between them at the nip or point of closest approach to each other. It is hot necessary to secure a good result that the sheet should hug the roll, as is at present the case, and by the arrangement indicated I am able to speed the rolls up to twice the maximum speed hitherto attainable without any detrimental effect to the rubber, for the latter is in'actual contact with the hot rolls for a very brief period.

The first effect of this invention'is to double the capacity of the mill. It is found that by the increase of speed the rolls do not be: come nearly so hot as they would with the sheet of rubber in close contact with the roll, thereby keeping the heat in the latter.

Further, the invention has the important advantage that when the operation of sheeting is concluded the operator with a single out can disengage the sheet and'remove it instantly without danger and without having touse force to disengage it. In this operation, again, a great saving of time is effected.

The invention can be carried out in different ways; but the most simple and practical plan is to employ small guide-rollers properly placed to receive the sheet as it passes through the rolls, to conduct it around one of the rolls, but out of contact therewith, and to return it again between the two rolls for fur ther action.

The accompanying drawings illustrate the best mode in which I have contemplated applying the principle of my invention.

Figure I of said drawings is a cross-section of a grinding-mill constructed in accordance with the invention, and Fig. II a similar view illustrating a modificatioh.

A B represent the two grinding or refining rolls, which are 3' cu rnaled in suitable bearings in side frames 0 and geared to rotate in opposite directions. In these respects the mill is of the common construction; but instead of forming the sheet in close and continuous contact with the back roll B in the usual way, it is guided entirely clear thereof after passing between it and the roll A. The small guiderollers a, Fig. I, are so located as to conduct the sheet I) around roller B and back through the nip of the grinding-rolls, as clearly shown in the drawings. These rollers a may be of any suitable material, as wood or iron.

To guide the sheet properly over the first roller a and to prevent its passing under the same, I prefer to place a doctor-blade c in the position shown, though its use is not indispensable.

Instead of employing a series of rolls for conducting the rubber sheet entirely around the back roll 13, the arrangement illustrated in Fig. II may be adopted. The sheet I), after passing between rolls A B, goes over the guideroller a beneath said rolls, and then passes around a curved guide g behind roll B, and finally over guide-roller a and between the sheeting-rolls again. Guide 9 is preferably a sheet of zinc, which is fastened to supporting-frame (I. Zinc is the preferred material, because its smooth surface creates but little friction when the rubber glides over it, and because, being a non-conductor of heat, it aids in preserving the rubber from injury.

It will be seen that by the use of this invention I avoid-the diiliculties and danger attending the use of ordinary grinding-mills, that the capacity of the mill is largely increased, and that when the operation is concludedthe removal of the rubber sheet may be easily and quicklyeifected, there being no possibility of its adhering to the rolls.

Having now fully described my said invention, what I claim is- 1. In a rubber grinding or sheeting mill, the combination, with the rolls, of guides for conducting the rubber sheet around one of said rolls out of contact therewith, substantially as described.

2. The combination, with the grinding and sheeting rolls, of guiding devices for conducting the rubber sheet around one of said rolls, said guidin g devices comprising rollers placed, respectively, above and beneath the nip of the rolls, and a curved smooth-surfaced sheet behind one of said rolls, substantially as described.

3. The combination of the grinding and sheeting rolls, the guides arranged around one of said rolls, and the doctor-blade for guiding the sheet over the first of said guide-rollers, substantially as described.

'In testimony whereof I have signed this specification inthe presence of two subscribing witnesses.

NATHANIEL CHAPMAN MITCHELL.

\Vitnesses:

E. M. 1\IIUNDY, JOEL ll. Lane. 

